U.S. patent number 6,591,162 [Application Number 09/641,032] was granted by the patent office on 2003-07-08 for smart load port with integrated carrier monitoring and fab-wide carrier management system.
This patent grant is currently assigned to Asyst Technologies, Inc.. Invention is credited to Raymond S. Martin.
United States Patent |
6,591,162 |
Martin |
July 8, 2003 |
Smart load port with integrated carrier monitoring and fab-wide
carrier management system
Abstract
A load port assembly capable of monitoring a plurality of
performance characteristics of wafer carriers. The load port
assembly may include one or more of the following monitoring
systems: a torque measurement system, a wafer height measurement
system, a carrier identification reader, an information pad, a
resistivity measurement system, a cleanliness measurement system, a
seal performance detector, and a relative humidity detector. In a
preferred embodiment of the present invention, each of the
monitoring systems are integrated into either a carrier advance
plate or a port door of the load port assembly.
Inventors: |
Martin; Raymond S. (Fremont,
CA) |
Assignee: |
Asyst Technologies, Inc.
(Fremont, CA)
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Family
ID: |
27093559 |
Appl.
No.: |
09/641,032 |
Filed: |
August 16, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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640463 |
Aug 15, 2000 |
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Current U.S.
Class: |
700/228;
700/225 |
Current CPC
Class: |
H01L
21/67242 (20130101); H01L 21/67253 (20130101); H01L
21/67265 (20130101); H01L 21/67294 (20130101); H01L
21/67379 (20130101); H01L 21/67775 (20130101) |
Current International
Class: |
H01L
21/67 (20060101); H01L 21/00 (20060101); H01L
21/673 (20060101); G06F 017/00 () |
Field of
Search: |
;707/3,104.1
;700/112,113,121,215,225,229,228,230,213 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"SMIF: A Technology for Wafer Cassette Transfer in VLSI
Manufacturing," by Mihir Parikh and Ulrich Kaempf, Solid State
Technology, Jul. 1984, pp. 111-115..
|
Primary Examiner: Choules; Jack
Attorney, Agent or Firm: O'Melveny & Myers LLP
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This application is a continuation in part of U.S. application Ser.
No. 09/640,463, filed Aug. 15 2000, now abandoned, which
application is incorporated by reference herein in its entirety.
Claims
What is claimed is:
1. A load port assembly capable of monitoring characteristics of a
carrier having a carrier door removably coupled to a carrier shell,
the load port assembly comprising: a port door having latch keys
capable of decoupling the carrier door from the carrier shell, said
port door includes: at least one monitoring system selected from a
group consisting of (i) a torque measurement system, and (ii) a
wafer height measurement system; a carrier advance plate having
registration pins for engaging the carrier shell while the carrier
is seated on said carrier advance plate, and capable of moving a
carrier seated upon said carrier advance plate towards said port
door, said carrier advance plate includes: at least two monitoring
systems selected from a group consisting of (i) a carrier
identification reader, (ii) a carrier configuration detector, (iii)
a resistivity measurement system, (iv) a cleanliness measurement
system, (v) a seal performance detector, and (vi) a relative
humidity detector.
2. The load port assembly according to claim 1, wherein said torque
measurement system is capable of measuring the amount of torque
required for said latch keys to decouple the carrier door from the
carrier shell.
3. The load port assembly according to claim 1, wherein said wafer
height measurement system is capable of detecting each wafer stored
in the carrier.
4. The load port assembly according to claim 1, wherein said seal
performance detector includes an inlet opening and an outlet
opening formed in said carrier advance plate that align with an
inlet and outlet valve located in the bottom of the carrier shell
when the carrier is seated on said carrier advance plate.
5. The load port assembly according to claim 1, wherein each said
monitoring system generates an electronic data signal.
6. The load port assembly according to claim 5, wherein the load
port assembly further includes a database for storing said
electronic data signals and generating reports.
7. A load port assembly capable of monitoring characteristics of a
wafer carrier having a carrier door coupled to a carrier shell, the
load port assembly comprising: a port door having latch keys to
engage the carrier door and decouple the carrier door from the
carrier shell, said port door includes: means for measuring the
torque required to decouple the carrier door from the carrier
shell; means for detecting each wafer stored in the carrier; a
carrier advance plate having registration pins for engaging the
carrier shell, and capable of moving a carrier seated upon said
carrier advance plate towards said port door, said carrier advance
plate includes: means for identifying the carrier; means for
determining if the carrier is compatible with the load port
assembly; means for neutralizing a static charge on the carrier;
means for measuring the amount of particulates within the carrier;
means for testing the effectiveness of the seal located between the
carrier door and the carrier shell; and means for measuring the
relative humidity within the carrier.
8. A load port assembly capable of monitoring characteristics of a
carrier having a carrier door coupled to a carrier shell, the load
port assembly comprising: a port door having latch keys to engage
the carrier door and decouple the carrier door from the carrier
shell, said port door includes: a torque measurement system; a
wafer height measurement system; a carrier advance plate having
registration pins for engaging the carrier shell while the carrier
is seated on said wafer advance plate, and capable of moving a
carrier seated upon said carrier advance plate towards said port
door, said carrier advance plate includes: a carrier identification
reader; a carrier configuration detector; a resistivity measurement
system; a cleanliness measurement system; a seal performance
detector; and a relative humidity detector.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the fabrication of integrated
circuits on semiconductor wafers, and in particular to a system
capable of monitoring a plurality of performance characteristics of
wafer carriers and to a system for managing carrier operation on a
fab-wide basis.
2. Description of Related Art
A SMIF system proposed by the Hewlett-Packard Company is disclosed
in U.S. Pat. Nos. 4,532,970 and 4,534,389. The purpose of a SMIF
system is to reduce particle fluxes onto semiconductor wafers
during storage and transport of the wafers through the
semiconductor fabrication process. This purpose is accomplished, in
part, by mechanically ensuring that during storage and transport,
the gaseous media (such as air or nitrogen) surrounding the wafers
is essentially stationary relative to the wafers, and by ensuring
that particles from the ambient environment do not enter the
immediate wafer environment.
A SMIF system has three main components: (1) minimum volume, sealed
carriers, or pods, used for storing and transporting wafers and/or
wafer cassettes; (2) an input/output (I/O) minienvironment located
on a semiconductor processing tool to provide a miniature clean
space (upon being filled with clean air) in which exposed wafers
and/or wafer cassettes may be transferred to and from the interior
of the processing tool; and (3) an interface for transferring the
wafers and/or wafer cassettes between the SMIF carriers and the
SMIF minienvironment without exposure of the wafers or cassettes to
particulates. Further details of one proposed SMIF system are
described in the paper entitled "SMIF: A TECHNOLOGY FOR WAFER
CASSETTE TRANSFER IN VLSI MANUFACTURING," by Mihir Parikh and
Ulrich Kaempf, Solid State Technology, July 1984, pp. 111-115.
Systems of the above type are concerned with particle sizes which
range from below 0.02 microns (.mu.m) to above 200 .mu.m. Particles
with these sizes can be very damaging in semiconductor processing
because of the small geometries employed in fabricating
semiconductor devices. Typical advanced semiconductor processes
today employ geometries which are one-half .mu.m and under.
Unwanted contamination particles which have geometries measuring
greater than 0.1 .mu.m substantially interfere with 1 .mu.m
geometry semiconductor devices. The trend, of course, is to have
smaller and smaller semiconductor processing geometries which today
in research and development labs approach 0.1 .mu.m and below. In
the future, geometries will become smaller and smaller and hence
smaller and smaller contamination particles and molecular
contaminants become of interest.
SMIF carriers are in general comprised of a carrier door which
mates with a carrier shell to provide a sealed environment in which
wafers may be stored and transferred. So called "bottom opening"
carriers are known, where the carrier door is horizontally provided
at the bottom of the carrier, and the wafers are supported in a
cassette which is in turn supported on the carrier door. It is also
known to provide "front opening" carriers, in which the carrier
door is located in a vertical plane, and the wafers are supported
either in a cassette mounted within the carrier shell, or to
shelves mounted in the carrier shell.
A typical wafer fab has several different types of tools into which
wafers from a carrier are loaded. Processing tools are used to form
patterned layers of silicon, silicon compounds and metals on the
wafer to define the individual IC devices. Metrology tools are used
for performing various tests on wafers to ensure the wafers are
fabricated to specification. Carrier cleaning tools are used to
periodically clean the interior surfaces of a carrier to remove
particulates and contaminants that accumulate within a carrier with
use. Another tool found in a wafer fab is a sorter, which performs
various functions including the transfer of wafers between the
various carriers positioned on the wafer sorter, the mapping of
wafer location within a carrier cassette, and wafer
identification.
In order to transfer wafers between a SMIF carrier and the various
tools within a wafer fab, a carrier is typically loaded either
manually or automatedly onto a load port assembly on a front of the
tool. Each load port assembly includes an access port which, in the
absence of a carrier, is covered by a port door. The SMIF carrier
is seated on the load port so that the carrier door and port door
lie juxtaposed to each other. In a front opening system, the
carrier is seated on a carrier advance plate which advances the
carrier to the port so that the respective carrier and port doors
lie adjacent to each other. Registration pins are provided on the
port door that mate with grooves in the carrier door to assure a
proper alignment of the carrier door with respect to the port
door.
Once the carrier is positioned against the port door, mechanisms
within the port door unlatch the carrier door from the carrier
shell and move the carrier door and port door together into the
process tool where the doors are then stowed away from the wafer
transfer path. The carrier shell remains in proximity to the
interface port so as to maintain a clean environment including the
interior of the process tool and the carrier shell around the
wafers. A wafer handling robot within the process tool may
thereafter access particular wafers supported in the carrier for
transfer between the carrier and the process tool.
Wafer carriers are manufactured to relatively narrow tolerances and
are tested prior to initial use within a wafer fab to ensure they
have been manufactured to specifications. However, carriers are
subject to wear, deformation, breakage and improper maintenance in
use, and several performance characteristics of each carrier should
be monitored over the life of the carrier as it transports various
wafer lots around the fab. These performance characteristics which
should be monitored include the following:
Seal Performance
One or more elastomeric seals are provided between the carrier
shell and the carrier door to prevent fluids from traveling into or
out of the carrier when the door is sealed within the shell. These
elastomeric seals wear over time and gradually become less
effective in isolating the environment within the carrier from the
environment surrounding the carrier.
Seal performance refers to how effective an elastomeric seal in a
carrier is at a given point in the life of a carrier at preventing
fluid flow around the seal between the carrier shell and carrier
door.
Cleanliness
Cleanliness relates to the amount of contaminants found within a
carrier at a given time. Contaminants may be grouped into two
classes, and there are different removal and monitoring systems for
each. The first type of contaminant includes relatively large
particles, for example bigger than 0.02.mu., which adhere to
surfaces within the carrier. These particles are generally removed
by injecting a cleaning solution onto the surfaces of the carrier
to flush away the particles. A second type of contaminant relates
to relatively small particles, for example smaller than 0.02.mu..
These particles may be airborne or adhered to surfaces. Such
smaller particles may be removed by including a particle filter
within the carrier, which removes particles that come into contact
with the filter as they float around the interior of the carrier.
These small particle contaminants are also removed from surfaces by
the cleaning solution injected into the carrier.
Sources of contaminants within a carrier include worn elastomeric
seals in a wafer carrier, fluids injected into the carrier and
instances where the carrier is opened for maintenance or other
purposes. As indicated above, it is important to monitor the
cleanliness of the interior of a carrier, as particles can
interfere with the device geometries formed on the wafers.
Relative Humidity
Wafer carriers are formed of various materials including plastics
such as polycarbonate which absorb moisture. Thus, after a carrier
is cleaned with a wet cleaning solution, it is common for the
carrier to have a higher relative humidity than ambient for days
after the cleaning. Humidity within a carrier can be a significant
source of damage to a semiconductor wafer.
Wafer Height
It is important that wafers within a carrier be located at a known
elevation relative to the load port and tool on which the carrier
is loaded so that a wafer handling robot can cleanly lift a wafer
off of a particular shelf and return a wafer to a particular shelf
without unintended contact with the wafer. However, over time,
factors such as carrier deformation, damage during use, improper
maintenance and/or being manufactured outside of specifications can
alter the height at which the shelves in the carrier are positioned
relative to the load port. It is therefore desirable to check the
position of the wafer support shelves within a carrier when a
carrier is loaded onto a load port.
Carrier Latching Force
In a front opening interface, in order to couple a carrier door and
carrier shell together, a mechanism in the port door rotates a pair
of hubs in the carrier door, which in turn cause latch plates to
extend into slots in the carrier shell. The latch plates also exert
a force on the carrier shell so that the carrier door and shell are
pulled tightly together. The same is true for bottom opening
systems, but such systems typically include a single, central
hub.
Front opening carriers further include a spring loaded mechanism
for biasing wafers toward a rear of the carrier (i.e., away from
the carrier door). Lying in contact with the edges of the wafers
within the carrier, the spring loaded mechanism exerts an
approximate 40 newton force against the carrier door. This force in
turn generates an additional force by the latch plates against the
carrier shell.
The force between the latch plates and carrier shell, and
consequently the torque required to rotate the hubs in order to
actuate the latch plates, can vary over time. It is important to
monitor this force, as significant variations can affect the
ability of the port door to couple and uncouple the carrier door
and shell.
Electrostatic Neutralization
Electrostatic build up on and discharge from wafers can damage or
destroy the wafers. Concern over electrostatic damage has been
increasing in recent years as device geometries get finer and the
requirements for reliability become more stringent. In conventional
carriers, it is known to provide a conductive path away from the
top and/or bottom surface of the wafer to neutralize electrostatic
charge on the wafers. Conductive coatings provided for neutralizing
the static charge may wear over time. Moreover, carriers may break,
or a conductive pathway may be broken if a carrier is reassembled
incorrectly during maintenance. It is therefore desirable to
monitor the ability of a carrier to neutralize static electric
charge.
Carrier Configuration Detector
A bottom surface of a carrier is generally provided with four
designated positions at which wells may be formed. Similarly, the
surface supporting a carrier at a load port assembly includes four
corresponding positions at which pins may be provided. These wells
on the bottom of a carrier can be used to define the type of
carrier and/or the type of process for which the carrier is
intended. For example, wafer fabs are often broken down into zones
for different fabrication processes, and carriers for one zone
should not be used in other zones. In this instance, wells could be
provided in the various positions on the bottom of the carrier to
designate a carrier for a particular zone. In practice, where a
carrier is used in a proper zone, the well(s) on the bottom of the
carrier match up with the pin(s) on the load port, and the carrier
seats properly on the load port. On the other hand, where a carrier
designated for one zone is used in another, incompatible zone, the
well(s) in the bottom of the carrier would not match up with the
pin(s) on the load port, and the carrier would not seat properly on
the load port.
The well(s) on the bottom of a carrier can be used to designate and
distinguish a carrier between a variety of other classifications,
such as for example designating a carrier as a 25 wafer carrier
versus a 13 wafer carrier; an enclosed SMIF carrier versus an open
cassette; a carrier supporting 300 mm wafers versus a carrier
supporting 200 mm wafers, etc. In each instance, the pins on a load
port will ensure that a carrier will only seat on a load port which
is designated to receive that type of carrier.
It is also known to provide a sensor within a well which generates
a signal when a pin seats within that well. Such a system provides
feedback as to whether the sensors on the bottom of a carrier in
fact match up with pins on the load port assembly. This system
provides an additional advantage that the sensors can distinguish
between a greater number of pin configurations on a load port, and
hence a greater number of different carrier configurations and
processes, than can the wells by themselves.
It would be advantageous to monitor situations where a carrier is
placed on a compatible load port and situations where a carrier is
placed on an incompatible load port, as well as the frequency of
both situations.
In addition to collecting data with regard to each of the
above-described performance characteristics of the carrier, it
would be useful to accumulate and analyze this data to improve and
optimize management of carrier operations throughout the wafer fab.
For example, this data could be used to analyze how various
performance characteristics of the carrier population change
overtime. This data can then be used to manage and maintain the
carrier population in an efficient manner, and also identify when a
carrier needs to be replaced.
SUMMARY OF THE INVENTION
It is therefore an advantage of the present invention to provide a
smart load port for capturing data relating to a plurality of
carrier and load port performance characteristics.
It is a further advantage of the present invention to store the
data on a central server for use in managing carrier operation
within the wafer fab.
It is a further advantage of the present invention to measure
several performance characteristics without impacting throughput of
wafers on a tool.
It is a further advantage of the present invention to ensure that
carriers are being cleaned properly and with the proper
frequency.
It is another advantage of the present invention to provide a
system which identifies when carrier seals begin to fail and when
the seals need to be replaced.
It is a further advantage of the present invention to identify the
relative humidity within a carrier at a given time and to determine
how carriers dry over time.
It is a further advantage of the present invention to provide
physical information pads to prevent location of a carrier
designated for one type of process on a load port for performing
another, incompatible process.
It is a still further advantage of the present invention to ensure
that wafer heights are within standard specifications.
These and other advantages are provided by the present invention
which in preferred embodiments relates to a system capable of
monitoring a plurality of performance characteristics of a wafer
carrier on a load port, and to a system for managing carrier
operation on a fab-wide basis. In particular, several detector and
measurement systems are built into or associated with the load port
assembly. These detector and measurement systems include a torque
measurement system, a wafer height measurement system, a carrier
identification reader, an information pad, a resistivity
measurement system, a cleanliness measurement system, a seal
performance detector and a relative humidity detector. These
monitoring systems can be provided on load ports associated with
various tools, such as processing tools, metrology tools, carrier
cleaning tools and sorters, to gather data relating to individual
carriers and the carrier population as a whole.
In accordance with further principals of the present invention, the
data gathered by the various measuring and detecting systems within
the load port assembly can be used to manage the carrier population
within the fab. For example, by monitoring a performance
characteristic over time, across the entire carrier population in
the wafer fab, the average change in that performance
characteristic over time may be accurately mapped for the
population in general. The standard deviation for the carrier
population with respect to that performance characteristic over
time may also be determined and stored.
This stored information can be used to provide valuable forecasting
information, which may be printed in report form, as to when the
average carrier or carrier subsystem would generally require
maintenance or replacement. This information can also be used to
identify carriers which are broken, have failed, or which are
performing outside of acceptable ranges for carriers of comparable
age. Moreover, the entire history of a carrier, for each of the
performance characteristics, can be stored. This promotes optimal
carrier management efficiency in that the optimal average timing
for maintenance and/or replacement of carriers is known. Moreover,
defective carriers may be quickly identified and removed from the
carrier population.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described with reference to the drawings,
in which:
FIG. 1 is a rear perspective view of a carrier for use with the
present invention;
FIG. 2 is a front perspective view of a load port assembly
including a plurality of monitoring systems according to the
present invention;
FIG. 3A is a schematic representation of a preferred embodiment of
a static neutralization system according to the present
invention;
FIG. 3B is a schematic representation of a further aspect of the
preferred embodiment of the static neutralization system according
to the present invention;
FIG. 4 is a perspective view of a height measurement system
according to the present invention;
FIG. 5 is a schematic representation of a seal performance detector
system according to the present invention;
FIG. 6 is a schematic representation of a relative humidity
detector system according to the present invention;
FIG. 7 is a schematic representation of a system architecture
according to the present invention;
FIG. 8 show sample reports that may generated in accordance with
the principles of the present invention;
FIG. 9 is an illustration of a bottom of a carrier including a well
configuration for designating the carrier for a particular
process.
DETAILED DESCRIPTION
The present invention will now be described with reference to FIGS.
1-9, which in preferred embodiments relate to a system capable of
monitoring a plurality of performance characteristics of a wafer
carrier, and to a system for managing carrier operation on a
fab-wide basis. While a monitoring system described hereinafter is
shown with respect to a front opening interface load port used with
a front opening unified pod ("FOUP"), it is understood that the
monitoring and management system according to the present invention
may alternatively be used with a bottom opening interface used with
bottom opening carriers. Moreover, while a carrier for 300 mm
wafers is shown, it is understood that the size of the carrier is
not critical to the present invention, and that the present
invention may be used with carriers of various sizes including
those adapted to transport 200 mm and 150 mm wafers.
It is further understood that preferred embodiments of the present
invention utilize SMIF technology, and comply with and allow
compliance with Semiconductor Equipment and Materials International
("SEMI") standards. However, alternative embodiments of the present
invention need not operate with SMIF technology and need not comply
with SEMI standards.
Referring now to FIG. 1, there is shown a perspective view of a
carrier 20 in the form of a 300 mm FOUP including a carrier door 22
mating with a carrier shell 24 to define a sealed environment for
one or more workpieces located therein. While carrier 20 is
illustrated as a 300 mm front opening carrier, as previously
indicated, the size and type of the carrier are not critical to the
present invention. Referring to FIGS. 1 and 2, in order to transfer
the workpieces between the carrier 20 and a tool 28, the carrier is
loaded onto a load port assembly 25 adjacent a port door 26 on a
front of the tool. Tool 28 may be any of a variety of tools in a
wafer fab including a process tool, a metrology tool, a carrier
cleaning tool and/or a sorter.
The carrier is loaded so that a rear surface 31 of the carrier door
22 faces a front surface 30 of the port door 26. The port door
includes a pair of latch keys 32 for being received in a
corresponding pair of slots 33 of a door latching assembly mounted
within carrier door 22. An example of a door latch assembly within
a carrier door adapted to receive and operate with latch keys 32 is
disclosed in U.S. Pat. No. 4,995,430 entitled "Sealable
Transportable Container Having Improved Latch Mechanism", to Bonora
et al., which patent is assigned to the owner of the present
invention, and which patent is incorporated by reference herein in
its entirety.
In order to latch the carrier door to the port door, the carrier 20
is manually or automatedly seated on a carrier advance plate 27.
The carrier advance plate 27 typically includes three kinematic
pins 29, or some other registration feature, which mate within
corresponding slots on the bottom surface of the carrier to define
a fixed and repeatable position of the bottom surface of the
carrier on the advance plate and load port assembly. The carrier
advance plate 27 is translationally mounted to advance the carrier
toward and away from the port door. Once a carrier is detected on
the carrier advance plate by sensors in the load port assembly, the
carrier is advanced toward the load port until the rear surface 31
of the carrier door 22 lies in contact with the front surface 30 of
the port door 26.
In addition to decoupling the carrier door from the carrier shell,
rotation of the latch keys 32 will also lock the keys into their
respective slots 33, thus coupling the carrier door to the port
door.
While a preferred embodiment of the door latch assembly in the
carrier door has been described above, it is understood that the
mechanisms in the carrier door for coupling/uncoupling the carrier
door to the carrier shell are not critical to the present invention
and may vary significantly in alternative embodiments.
Load port assembly 25 further includes a plurality of monitoring
systems for monitoring a plurality of performance characteristics
of carrier 20 and/or load port assembly 25. These systems include a
torque measurement system 38, a wafer height measurement system 40,
a carrier identification reader 42, a carrier configuration
detector 44, a resistivity measurement system 46, a cleanliness
measurement system 48, a seal performance detector 50, and a
relative humidity detector 52. Each of these measurement systems
and detectors are shown in FIG. 2, schematically or otherwise, and
described in greater detail below. In addition to performance
characteristic monitoring systems, the load port assembly 25
further includes a graphical user interface for user input and
system feedback.
Torque Measurement System
As discussed in the Background of the Invention section, it is
desirable to measure the amount of torque required to rotate the
pair of latching hubs to thereby couple and decouple the carrier
door and shell. If the torque is too high, this can interfere with
proper opening and closing of the carrier 20. The present invention
therefore includes a torque measurement system 38 mounted to one or
both of the latch keys 32. The torque measurement system may be
mounted on the back side of the port door, and may include any of
various known mechanisms for measuring the torque exerted by and/or
on a rotating object such as the latching hubs.
The torque measurement system may be included on load ports at
various tools, including for example processing tools, metrology
tools, wafer cleaning tools and sorters.
Wafer Height Measurement System
It is desirable to measure the height of the wafer support shelves
(not shown) within carrier 20 relative to registration pins 29. If
a carrier is improperly manufactured, or where a carrier 20 has
become deformed, the height of the shelves and wafers will vary
from the anticipated height. This variance may result in undesired
contact between a wafer and a wafer handling robot upon removal of
the wafer from the carrier and/or undesired contact between the
wafer and the shelf upon return of the wafer to the carrier.
As such, the present invention includes the wafer height
measurement system 40 for measuring the height of the wafers within
the carrier 20 relative to the registration pins 29 on which the
carrier 20 is supported. The wafer height measurement system may
comprise any of various known wafer mapping systems, such as for
example that disclosed in U.S. patent application Ser. No.
09/173,710 entitled "Wafer Mapping System" to Rosenquist, et al.,
which application is assigned to the owner of the present invention
and which application is incorporated by reference herein in its
entirety.
As disclosed in the incorporated reference and as shown in FIG. 4
of the present invention, one embodiment of the wafer height
measuring system detects wafer height position as the port door 26
is lowered away from the access port of tool 28 in order to allow
wafer transfer through the port. According to the embodiment shown
in FIG. 4, the wafer height measurement system 40 includes a pair
of fingers 54 rotatably mounted to the top of the port door. In a
retracted position, the fingers lie above and behind the port door.
However, once the port door is lowered sufficiently to avoid
contact between the fingers and the carrier shell, the fingers are
rotated to their extended position into the carrier shell via a
motor 56 and actuation assembly 58.
The wafer height measuring system 40 further includes a transmitter
and receiver 60 and 62 either mounted in the port door or at the
ends of the fingers (as shown in FIG. 4). In their extended
position, the fingers transmit a beam of electromagnetic energy
from the transmitter across a front of the carrier shell to the
receiver. As the port door and wafer height measuring system move
downward, the wafers 64 within the carrier will break the beam and
prevent receipt of the beam in the receiver. At this time, the
elevation of the wafer will match the known elevation of the beam
so that the position of the wafer at this point may be measured and
mapped in memory. The duration of time the beam is blocked may also
identify a cross-slotted and double-slotted wafer.
In the embodiment shown in FIG. 4, the fingers are provided to
detect the position of wafers 64 seated on shelves within the
carrier shell 24. As would be appreciated by those of skill in the
art, the position and configuration of fingers 54 may be altered,
depending on the carrier configuration, so as to instead detect the
position of a shelf within the carrier 24. Thus, the height of
shelves not including a wafer 64 may also be detected. As would be
appreciated by those of skill in the art, a wide variety of other
wafer height measuring systems of known construction may be
employed to detect the height of a wafer and/or wafer shelf within
carrier shell 24.
In a preferred embodiment, the wafer height measuring system 40 may
be employed on a tool 28 such as processing tools, metrology tools,
carrier cleaning tools, and sorters so as to determine the height
of the wafers and/or shelves within the wafer carrier.
Carrier Identification Reader
Carrier identification reader 42 is mounted on load port assembly
25 so as to scan, read or otherwise identify a unique
identification mark associated with each carrier 20. Carrier
identification mark and identification reader systems are well
known in the art and comprise, for example, a bar code on carrier
20 and a bar code reader mounted on the load port. It is further
understood that the carrier identification reader 42 may be located
remotely from load port assembly 25. In such an embodiment, the
identification of a particular carrier on a particular load port
assembly is transmitted to a remote receiver which identifies the
mark and confirms that particular carrier is appropriate for that
particular load port. Such a system includes an RF pill mounted on
the carrier, which pill includes a transponder for transmitting
information relating to the carrier and/or wafers contained therein
to a storage and control system. Such RF pills, and the systems
making use thereof, are described for example in U.S. Pat. Nos.
4,827,110 and 4,888,473 to Rossi, et al., and U.S. Pat. No.
5,339,074 to Shindley. The carrier may alternatively include an IR
tag. Such IR tags, and systems making use thereof, are described
for example in U.S. Pat. Nos. 5,097,421, 4,974,166 and 5,166,884 to
Maney, et al. Each of the above-identified patents is assigned to
the owner of the present invention and each is incorporated by
reference in its entirety herein. As would be appreciated by those
of skill in the art, other known carrier and/or wafer
identification and identification reader systems may be used in the
present invention to indicate that a particular carrier 20 is
properly seated on a particular load port assembly 25.
The carrier identification reader 42 as described above may be used
on various tools 28 including for example processing tools,
metrology tools, carrier cleaning tools, and sorters.
Carrier Configuration Detector
As discussed in the Background section, it is a conventional
protocol to make use of wells or sensors on the bottom of a carrier
and information pads, such as for example pins, on a carrier
advance plate to ensure that when a carrier is placed on a load
port, that carrier is in fact compatible with that load port. As an
example, carriers that are used to transport wafers to and from a
process tool performing a copper deposition step must not also be
used on process tools performing gate oxidation, or many other
process steps. If the carrier used in the copper process were also
used in a gate oxidation process, the copper may chemically react
and cross-contamination within the container may occur. Thus,
carriers designated for copper deposition processes include a well
configuration on their bottom surface including a plurality of
wells 80 such as for example shown in FIG. 9 that will seat on load
ports that are compatible with copper deposition processes, but
will not seat on load ports that are incompatible with copper
deposition processes. As shown in FIG. 9, a well 80 is provided at
positions A, B and D, but not at position C.
Ideally, the carrier identification reader 42 prevents the use of
carriers on incompatible processes. However, in order to provide
redundancy, the well--pin protocol may also used.
In accordance with the present invention, sensors may be provided
within the wells on the bottom of the carrier to generate feedback
as to when a carrier is seated on a compatible load port, and may
also generate feedback as to when a carrier is seated on an
incompatible load port. Namely, where all of the number and
location of pins match the number and location of sensors in the
wells, feedback is generated to indicate that the carrier is
compatible with that load port. On the other hand, where either the
number or position of the pins do not match the number or position
of the sensors in the wells, feedback is generated to indicate that
the carrier is incompatible with that load port.
In addition to providing such feedback, the sensors may physically
block a pin from seating in a well where the pin--well
configurations are not compatible. Thus, the system according to
the present invention both blocks a carrier from properly seating
on an incompatible load port and provides sensory feedback as to
the incompatibility. The sensors of the prior art did not
physically block a carrier from seating on an incompatible load
port.
It is understood that the various well configurations on the bottom
of a carrier can be formed by fabricating a carrier with four wells
and then plugging select wells to designate a carrier for a
particular configuration. This provides an advantage in that a
carrier can be configurable by the wafer manufacturer.
Alternatively, the different well configurations can be formed
during the injection molding process when the bottom plate of the
carrier is formed.
As would be appreciated by those of skill in the art, the
compatibility detector 44 on load port 25 may take on a wide
variety of configurations to designate a wide variety of
compatibility protocols, especially where the protocol involves
sensors in the wells in the bottom of a carrier. Moreover, the
information pads of compatibility detector 44 can take on a wide
variety of shapes other than pins, which shapes generally
correspond to the shape of a recessed portion in the bottom of a
carrier.
Seal Performance Detector
As indicated in the Background of the Invention section, it is
desirable to be able to test the effectiveness of the elastomeric
seal between the carrier door and the carrier shell when the
carrier is sealed. As such, in accordance with a further aspect of
the present invention shown in FIG. 5, a load port assembly 25 in
accordance with the present invention may further include a seal
performance detector 50. The seal performance detector 50 is
preferably used with a load port including an inlet opening 70 and
an outlet opening 72 formed in the carrier advance plate 27 as
shown for example in FIG. 2. In such an embodiment, the carrier 20
may include inlet and outlet valves (not shown) of known
construction which seat on top of inlet 70 and outlet 72,
respectively, when carrier 20 is seated on load port assembly
25.
Which such a construction, a fluid may be injected into carrier 20
through inlet opening 70 and the inlet valve and may be drawn from
the carrier 20 through the outlet valve and outlet opening 72. The
inlet and outlet openings may further include a seal to facilitate
fluid flow from the inlet opening through the carrier and out the
outlet opening. Such seals, and the valves provided in the carrier,
are shown for example in U.S. Pat. No. 6,056,026 entitled
"Passively Activated Valve For Carrier Purging" to Fosnight, et
al., which patent is assigned to the owner of the present invention
and which patent is incorporated by reference herein in its
entirety.
FIG. 5 is a schematic representation of the seal performance
detector 50 for use in accordance with the present invention. The
seal performance detector 50 includes a flexible inlet hose 74
affixed to the inlet 70 through the carrier advance plate for
supplying a flow of ultraclean air or nitrogen from a house supply
76 located adjacent to or remote from load port assembly 25. In a
preferred embodiment, fluid from house supply 76 is filtered
through first and second filters 78 and 80 prior to entering
carrier 20. Filters 78 and 80 may be chemical and/or HEPA filters.
Seal performance detector 50 further includes a flow meter 82 for
measuring a flow rate of fluid into carrier 20, and a valve 84 for
controlling the fluid flow rate into carrier 20. Seal performance
detector 50 further includes a flexible outlet hose 86 affixed to
outlet opening 72 through the carrier advance plate, and a pressure
gauge 88 mounted adjacent to or remote from load port assembly
25.
In one embodiment of operation, the seal performance detector
performs in two different modes: one where there is a high leak
rate around the seal and one where there is a low leak rate around
the seal. For both, fluid is initially injected into the carrier
through the inlet hose 74 and inlet 70 at a constant rate. As the
pressure within the carrier increases, the pressure measured by
gauge 88 will similarly increase. Where there is a high leak rate
around the seal, as the pressure increases, the amount of fluid
escaping around the seal will quickly equal the amount of fluid
injected into the carrier. When this point is reached, the pressure
gauge will read a constant pressure. The point at which the
pressure gauge remains constant is then recorded for that
carrier.
Where a seal is performing well, and there is a low leak rate, the
pressure in the carrier will continue to rise upon the constant
flow rate of fluid into the carrier through inlet 70. In order to
prevent a situation where the pressure within a carrier would
exceeds a pressure within the carrier during normal operation, when
the pressure exceeds a predetermined reference pressure, the flow
rate of fluid into the carrier is then decreased. As the flow rate
of fluid into the carrier is decreased, at some point, the flow
rate into the carrier will equal the flow rate around the seal. At
this point, the pressure gauge will read a constant pressure. The
point at which the pressure gauge remains constant is then recorded
for that carrier.
It is understood that other known methods may be used to measure
the leak rate around a seal in alternative embodiments.
Using the seal performance detector 50 on a regular basis will
indicate how the elastomeric seal wears over time. Additionally,
leak rates over predetermined levels, for example 3.5 liters per
second, may indicate that the seal needs to be replaced.
Seal performance detector 50 may be used on various tools 28
including for example metrology tools, carrier cleaning tools, and
sorters. Additionally, detector 50 could be utilized on stand alone
purging stations as well as storage shelves within a stocker.
Relative Humidity Detector
The relative humidity detector 52 will now be described with
reference to the schematic illustration of FIG. 6. Detector 52 can
make use of the flexible hose 74, the source 76, the filters 78 and
80, the flow meter 82 and the valve 84 used by the seal performance
detector 50 and connected to inlet 70 on load port assembly 25. For
this embodiment, house supply 76 preferably provides dry air with
either no moisture content, or a low, known moisture content.
Relative humidity detector 52 further includes a vacuum pump 86
affixed to outlet 72 in the load port assembly 25 via a flexible
hose 88. It is understood that vacuum pump 86 may be omitted in
alternative embodiments. Detector 52 also includes a meter such as
a barometer 90 for measuring the relative humidity of the fluid
drawn from the carrier 20 through hose 88, and a valve 92 for
controlling the flow of the fluid drawn from the carrier. By
injecting a known volume of dry gas of known relative humidity into
carrier 20, and measuring the relative humidity of the volume of
gas purged from the carrier, the relative humidity within the
carrier may be determined.
Relative humidity detector 52 may be used on various tools 28
including for example metrology tools, carrier cleaning tools, and
sorters. Additionally, detector 52 could be utilized on stand alone
purging stations as well as storage shelves within a stocker. Where
the relative humidity detector 52 is used on high throughput tools,
it is used substantially as a measurement device. However, where
the detector 52 is used on a testing device, where a carrier may
remain for prolonged periods, the detector 52 may also be used a
conditioning device which actually removes humidity from a carrier.
In this instance, the detector can map how humidity within a
carrier changes over time, which information can be stored for
later use.
Static Neutralization Measurement System
A ground path circuit is provided to neutralize electric charge
from the wafers. In particular, in one carrier configuration for
carriers seated on a load port, an electric path from the wafers is
provided through the wafer support shelf, through the carrier
shell, to the handle on top of the carrier. The carrier handle is
in turn electrically coupled to the kinematic plate which rests
atop the electrically grounded registration pins on the load port
assembly. It is also desirable to neutralize static charge where a
carrier is being transported by an overhead transport system which
grips the carrier by the handle. In this instance, the ground path
circuit is as described above, but the charge is neutralized
through the overhead transport in contact with the handle. It is
understood that a carrier may include other ground paths.
The static neutralization measurement system 46 is provided to test
the ability of a carrier to neutralize static buildup. In one
embodiment (FIG. 3A), the system 46 measures resistance by passing
a known current from a known voltage source through a path and
testing the resulting resistivity. If the resistivity is too high,
or if there is no current flow, the carrier needs to be repaired or
replaced. The static neutralization measurement system in this
embodiment includes a dummy wafer 82 supported on an end effector
84 of a wafer handling robot or seated within the carrier 20 (as
shown). The wafer handling robot is connected to a current source
via wire 86 and provides the current to the dummy wafer. The wafers
being processed are preferably removed from a carrier, and the
dummy wafer is inserted into the carrier. The current from the
dummy wafer is then passed through the ground path circuit. In one
embodiment emulating a carrier on a load port, the current is
passed through the registration pins and the resistance is measured
by, for example, an ohmmeter 88.
In another embodiment emulating a carrier being transported on an
overhead transport system (FIG. 3B), an arm can be provided which
contacts the handle so that the current is passed through the
handle to the arm and measured.
It is understood that other known systems may be used to measure
the ability of a carrier to neutralize static electric charge. Such
other known systems include a charge plate on the load port which
charges a carrier with a current and measures how long it takes to
dissipate the charge. It is also understood that the measurement
system 42 may measure other electrical properties of a carrier. For
example, it may be that a carrier acts as a Faraday cage. In this
instance, the effectiveness of the Faraday cage can be measured by
the system 42.
In embodiments where the system measures resistance, resistance can
be measured by a conventional resistance measuring device such as
an ohmmeter included in the circuit. The change in the measured
resistance for a carrier over time can be stored, and carriers
having a resistance that is too high or no current flow can be
replaced or repaired. Similarly, where the static neutralization
measurement system 46 measures static neutralization by other
methods, these measurements are taken over time and stored, and if
the measurement indicates that static neutralization from the
carrier is poor or nonexistent, the carrier can be repaired or
replaced.
The static neutralization measurement system 46 may be used on
various tools 28 including for example metrology tools and
sorters.
Cleanliness Measurement System
Cleanliness measurement system 48 may in fact comprise two separate
cleanliness measurement subsystems. The first subsystem measures
relatively large particles. In general, these particles may be
removed by a carrier cleaning system, such as for example that
disclosed in U.S. Pat. No. 5,846,338, entitled "Method And
Apparatus For Dry Cleaning Room Containers" issued Dec. 8, 1998,
which patent is assigned to the owner of the present invention, and
which patent is incorporated by reference herein in its entirety.
That patent discloses using an ultraclean CO.sub.2 aerosol or
ionized nitrogen gas sprayed onto the interior surfaces of a
carrier to remove contaminants from those surfaces. The contaminant
cleanliness measurement subsystem may operate by collecting the
aerosol or gas after it has been sprayed into the carrier, and
performing a particle analysis to identify and quantify the amount
of particles found in the aerosol or gas. The analysis may be
performed remote from the load port, but the carrier from which the
aerosol or gas was taken is noted, and the results of the analysis
are later linked to the carrier from which the aerosol was
taken.
It is understood that the contaminant cleanliness measurement
subsystem for detecting relatively large particles may operate in
conjunction with various other cleaning systems, wet or dry, with
the cleaning solution being analyzed after it has removed
particulates and contaminants from the interior carrier
surfaces.
The cleanliness measurement system 48 further includes a subsystem
for measuring relatively small particles, such as airborne
molecular contaminants (AMC). It is known to provide mechanisms
within a carrier for removing airborne molecular contaminants from
the interior of a carrier. Such mechanisms include particle filters
which are affixed to a surface within a carrier which capture
airborne molecular contaminants as they randomly contact the
filter. Such a filter is disclosed for example in U.S. Pat. No.
4,724,874, entitled "Sealable Transportable Container Having A
Particle Filtering System" to Parikh et al., which patent is
assigned to the owner of the present invention and which patent is
incorporated herein by reference. These filters get dirty over time
and must be periodically removed and replaced by a new filter. The
AMC measurement subsystem may operate in conjunction with the
particle filtering system so that when the filter is removed, a
chemical analysis may be performed on the filter to determine the
identity and quantity of airborne molecular contaminants captured
by the filter over a given period of time.
Although not critical to the present invention, in one embodiment,
the filter may include a magnet so that the filter may be easily
affixed to an interior surface of the carrier, and may be easily
removed from the carrier by an end effector including an
electromagnet or permanent magnet of sufficient coercivity to
overcome the attractive forces of the filter magnet with the
carrier surface. Once removed, the end effector may transfer the
filter to the AMC measurement subsystem for analysis.
The date, filter identification and carrier from which the filter
is removed is stored. Then, after the filter analysis is performed,
the analysis is matched with the filter and stored, so that the
results may be associated with the carrier from which the filter
was taken.
It is understood that various other AMC removal techniques may be
used with the AMC measurement subsystem according to the present
invention. Moreover, it is understood that a great many other
onboard monitoring devices may be provided within the carrier, and
removed at a load port for analysis as described above. Such
systems include a surface acoustic wave monitor chip, a shock and
vibration monitor, a temperature monitor, a humidity monitor, an
oxygen monitor and a desicant to name a few.
In accordance with further principals of the present invention, the
data gathered by the various measuring and detecting systems
associated with the load port assembly 25 can be used to manage the
carrier population within the fab. For example, by monitoring a
performance characteristic over time, across the entire carrier
population in the wafer fab, the average change in that performance
characteristic over time may be accurately mapped for the
population in general. The standard deviation for the carrier
population with respect to that performance characteristic over
time may also be determined and stored.
This stored information can be used to provide valuable forecasting
information, which may be printed in report form, as to when the
average carrier or carrier subsystem would generally require
maintenance or replacement. This information can also be used to
identify carriers which are broken, have failed, or which are
performing outside of acceptable ranges for carriers of comparable
age. Moreover, the entire history of a carrier, for each of the
performance characteristics, can be stored. This promotes optimal
carrier management efficiency in that the optimal average timing
for maintenance and/or replacement of carriers is known. Moreover,
defective carriers may be quickly identified and removed from the
carrier population.
A system architecture for gathering this information is shown in
FIG. 7. As shown therein, the torque measurement system 38, wafer
height measurement system 40, resistivity measurement system 46,
cleanliness measurement system 48, seal performance detector 50,
and a relative humidity detector 52 associated with load port
assembly 25 each gather data relating to a particular performance
characteristic as described above. Once data is generated for a
particular carrier, that data is forwarded, along with the carrier
identification and a date and time stamp, to a central server
database 100 for the wafer fab. The carrier identification and
date/time stamp may be generated by the carrier identification
system 42 as described above. It is understood that this data may
be for carriers within a particular wafer fab. Alternatively, it is
understood that a server may be linked to several wafer fabs to
gather information about the various carriers in each fab.
It is further understood that the various detector and measurement
systems need not all generate data that is sent to the server 100
at the same time. Data may instead be forwarded to the server 100
with a carrier identification and time stamp from some detector and
measurement systems and not others. This occurs for example where a
load port is not equipped with all of the above-described
measure.
Once data is stored in the database 100, the database can generate
a wide variety of reports 102 relating to carrier history, one or
more performance characteristics for a particular carrier and/or
one or more performance characteristics for the entire carrier
population. Database software is well known for taking the data
entered from the various monitoring systems and generating the
desired reports therefrom. Some sample reports are shown in FIG. 8.
A first report 102 shows the seal performance, or leak rate, for a
particular carrier, carrier #12579. As shown therein, the seal for
carrier 12579 was performing well until June 15, at which time the
measured conductance was found to be outside of acceptable limits,
thus requiring maintenance or replacement of the carrier. A second
report 102 shows average slot pitch between carrier shelves for the
population of carriers. The report shows that most carriers (about
50) have an optimal pitch of about 9.9 mm. Ideally, the bell curve
would be narrow (i.e., low standard deviation, with numbers
dropping off quickly for carriers having less than or greater than
the optimal pitch). A wide bell curve indicates that in general the
slot pitch in the carrier population was manufactured with poor
tolerances and/or there is a high deformation rate. A third report
102 shows latch torque required to actuate the latches for the
population of carriers. As shown, the majority of carriers (about
36) require a latching force of 1.75 Newton-meters to actuate the
latches. Again, it is desirable to have a narrow bell curve. There
is also shown a carrier which was measured as requiring a latch
force above 2.5 Newton-meters. This report indicates that that
carrier needs to be repaired or replaced.
It is understood that reports for each performance characteristic,
both for individual carriers, and the whole carrier population, may
be generated from database 100.
Although the invention has been described in detail herein, it
should be understood that the invention is not limited to the
embodiments herein disclosed. Various changes, substitutions and
modifications may be made thereto by those skilled in the art
without departing from the spirit or scope of the invention as
described and defined by the appended claims.
* * * * *